Dental crown restorations traditionally have been fabricated from precious metals and alloys, porcelain fused to metal, and to a smaller degree, all-ceramic or porcelain. Materials used for dental crown restorations have changed over the past 10 years. To date, 20% of all dental crown restorations are fabricated with all-ceramic materials—and this market is growing.
Porcelain veneer restorations are also fabricated with all-ceramic materials and have steadily grown in popularity in the last twenty years. For the purpose of definition, porcelain veneers, all-ceramic crowns, or dental restorations fabricated from porcelain, ceramic or ceramic-like materials are referred to as all-ceramic dental restorations. All-ceramic dental restorations are made upon the order of a dentist by a dental laboratory technician.
The dentist takes a dental impression of the teeth to be restored. The dental impression is then filled with dental stone to fabricate a stone model that replicates the tooth or teeth to be restored. Typically, at this stage, the stone working model is used by the dental laboratory technician to begin the necessary steps to fabricate the all-ceramic dental restoration to fit the prepared tooth or teeth. The stone model is deemed the “working model”; the working model is sectioned into individual working dies to replicate the tooth or teeth to be restored. Dental ceramic material is milled or pressed into the designated shape based upon the working dies, and is subsequently finished and contoured to fit on the working dental model.
During final fabrication of all-ceramic restorations, a 30-50 micron space or gap exists between the all-ceramic restoration and the working stone die. This gap replicates the space that will be occupied by a cement, luting, or bonding material when the restoration is permanently adhered to the tooth in the mouth. In comparison, the fabrication process for all-metal or porcelain-fused-to-metal dental crown restorations yields a more intimate fit of approximately 20 microns to the working stone die on the working models, and subsequently the prepared tooth. Thus, the fit of all-ceramic restorations differs from that of metal or porcelain-fused to metal restorations in that the all-ceramic restoration fits the working stone die, and subsequently the prepared tooth, with a larger space of 30-50 microns. A problem arises in the final finishing and contouring stage of all-ceramic crown fabrication due to the 30-50 micron space between the all-ceramic restoration and the working die. Due to the 30-50 micron gap, the all-ceramic restorations fall off of their respective dies during the finishing and contouring process and it is difficult to keep them in place on the working dies in order to complete the finishing and contouring procedure. This same problem exists when the dentist places the all-ceramic restorations on the prepared teeth in the mouth during the process of evaluating external contour and color, making any re-contouring adjustments and/or polishing before final cementation, luting or bonding of the restorations to the teeth.
Since the inception of all-ceramic restorations, many methods have been tried to keep the all-ceramic restorations temporarily secured to their respective working dies on the working model during finishing and contouring in the dental laboratory setting. Materials that have been used to temporarily adhere the all-ceramic restoration to the die often stick to the restoration and contaminate the ceramic and/or it is time consuming to remove these materials from the all-ceramic restoration and the working stone die.
Additionally, in the dental office setting, it is common practice to make use of a water-soluble try-in paste that allows the dentist and patient to judge what the final color of the all-ceramic restoration will look like before it is permanently adhered to the tooth. The try-in paste is tooth-colored and incapable of adhering to the tooth surface or the all-ceramic restoration. Typically, the color of the try-in paste matches the color of the cement or luting material that will be used to permanently adhere the all-ceramic restoration to the prepared tooth. For nearly twenty years try-in pastes have been available from several companies in the dental market. The primary problem with use of the try-in paste is that the paste will marginally hold the all-ceramic restoration in place on the prepared tooth for only a very limited amount of time, making it difficult to assess color and fit before the restorations dislodge, which increases the risk of breakage before they are permanently adhered to the prepared tooth.